A battery monitoring unit (1) includes a control IC (10), a CPU (20), and a load circuit (30). In the inside of the battery monitoring unit 1, the control IC (10) and the CPU (20) each of which is a control circuit are connected to a unit internal ground (GND2) that is common thereto. The load circuit (30) is connected to a power ground (P-GND) different from the unit internal ground (GND2). In the inside of the battery monitoring unit (1), the power ground (P-GND) and the unit internal ground (GND2) are connected with each other via a diode (50). The unit internal ground (GND2) and the power ground (P-GND) are connected to an external ground (GND1) that is common thereto via an electric wire extending from a first ground terminal (41) and an electric wire extending from a second ground terminal (42), respectively. Thus, even when a disconnection has occurred between the battery monitoring unit and the external ground, the function of the battery monitoring unit is prevented from losing.
